Linux as an RTOS

Linux success in the embedded space is well established. In October 2007, VDC
reported that Linux held a 40% share among embedded operating system
choices by system developers. Smaller share slices were held by commercial
OS vendors, in-house, “other” and “no formal OS”. In the Linux wedge, free
Linux distributions outpaced paid ones by more than two to one. And, the free
side was trending upward, with free distros outpacing paid ones by more
than four to one among future embedded project deployment plans.

But, that's just one source of stats. More recently, Embedded Market
Forecasters (EMF) came out with a report titled “Embedded Linux Total
Cost of Development Analyzed”, which it says is based on interviews with
more than 1,300 embedded developers. In its summary, EMF reported the
following:

“Embedded Linux has achieved design parity with commercial RTOSes for most
projects.”

“Embedded Linux design outcomes are consistent with the outcomes
of projects using OSes from commercial RTOS vendors.”

“Use of a commercial embedded Linux OS is more effective than a
noncommercial 'in-house' Linux development undertaking.”

“Embedded
Linux can be used in a mission-critical environment that requires MILS
(Multiple Independent Levels of Security) or EAL (Evaluation Assurance
Level) certification or POSIX (Portable Operating System Interface)
conformance, when used in protected memory under a certified RTOS.”

Dr Jerry Krasner, President of EMF and author of the report, said, “This
study shows that designing with an embedded Linux OS can be as dependable
as designing with an RTOS.”

Distro Share Distribution

Linux Counter (counter.li.org) has been keeping track of many things for
many years. One of those things is distro share percentages. Here is how they
stacked up, as of December 9, 2007. The data is derived from 147,964
registrations entered and 151,087 values.

Distro Share Percentages

Distribution

Count

Percent

CentOS

1,190

0.80%

Debian

28,949

19.56%

Fedora Core

10,451

7.06%

Gentoo

12,642

8.54%

Kubuntu

1,837

1.24%

Mandrake

7,602

5.14%

Mandriva

2,870

1.94%

Red Hat

11,349

7.67%

SUSE

14,757

9.97%

Slackware

13,166

8.90%

Ubuntu

19,490

13.17%

Others

26,783

18.10%

What Are They Using?

Each month, we'll be featuring a fun Linux implementation by a notable user.
Launching the series is Wendy Selzer. A founder of Openlaw, its open DVD
forum and the Digital Effects Clearing House, she also was a star attorney
with the Electronic Frontier Foundation, where she led EFF's Digital
Television Liberation Front, fighting restrictive government technology
mandates with open-source software. These days, she lives near Boston, where
she serves as assistant professor at Northeastern University School of Law
and fellow with the Berkman Center for Internet and Society at Harvard Law
School.

Here's Wendy:

I'm using MythTV to power my home entertainment system. The combination
digital video recorder, jukebox, streaming audio server and Web browser is
a Debian-based Pentium 4 running MythTV and other free software.

I built this machine when the Broadcast Flag was threatening the continued
availability of open high-definition television tuners, but since public
interest groups (including the American Library Association, Electronic
Frontier Foundation and Public Knowledge) defeated the
Broadcast Flag, the hardware is still available, and Moore's Law makes it
cheaper all the time. (Full specs at wendy.seltzer.org/mythtv;
the large-screen TVs pictured aren't mine.)

The DVR picks up over-the-air television in HD and standard def, recording
a mix of programs I've directly selected, TiVo-like “season
passes” and
those it gleans from searches or community-generated lists. Whenever a
“best movie of all time” or nature program comes up, I can time-shift it to
fit my schedule. If I'd rather watch the “NewsHour” in half an hour, I can
time-squeeze it to fit. Independent video from YouTube and Miro round out
the mix.

Ripping my CDs to lossless FLAC files gives me a jukebox from which I can
select playlists to listen to on my living-room stereo, stream to the study or
office, or move to a pocket. I can record the Metropolitan Opera's Saturday
matinee broadcasts (streamripper from a crontab) and pull up Wikipedia
pages or libretti alongside.

The system that started as a political statement has become immensely
practical (and fun). The general-purpose computer lets me watch media as I
want to see or hear it. We just have to make sure the media stays
unencumbered and the technologies aren't hampered by ill-designed mandates
from Hollywood.

diff -u: What's New in Kernel Development

The 2.4 kernel looks more and more immobile. Except for bug fixes, it
no longer seems to be the case that any new code will be accepted.
Even clean, well-written, minimally invasive driver ports from the 2.6
tree now are being turned away, as Vitaliy
Ivanov recently discovered.
He'd ported the adutux driver to 2.4 and submitted it, only to be told
by Willy Tarreau that the driver would not
be accepted, because no one
used the relevant hardware on 2.4 systems. The fact that this may be
because the driver has not been available was met with the argument
that people who may have needed such a driver probably already
have found different hardware to solve their problem. And, Willy added,
because the 2.4 tree was not changing so quickly these days, those who
did want the patch would have no trouble applying it themselves.

Vitaliy was a bit disappointed and surprised by this. But, in spite of
the rejection, Willy and other top hackers still helped Vitaliy get
the patch into the best possible shape, in case anyone ever did want to
apply it. The patch apparently now will live in Willy's own personal
tree, which gathers together 2.4 patches that are unlikely to make it
into the official tree.

The hardware4linux.info site has come on-line, providing a database of
hardware and its interoperability with the various Linux
distributions that exist in the wild. Like similar projects, this one
relies on user-contributed data.

It's possible that the Linux-tiny Project will be started up again,
under Michael Opdenacker's leadership, but there seems to be
considerable opposition. Linux-tiny is a general effort to make the
kernel smaller, both in RAM and on disk, and to provide a central
location to submit all such patches, so they can be fed to Andrew
Morton or Linus Torvalds. But, several folks, including Andrew, felt
there was no need for a central location beyond the kernel itself. His
feeling is that any patches that can help make the kernel smaller
should be submitted to him, rather than to Michael or anybody else.

However, as a lot of these patches already have collected around
Michael, he feels he's still needed to help organize them and present
them to Andrew or whomever. So, there does seem to be the sense that
Linux-tiny is needed, in spite of the fact that folks like Andrew are
very much opposed. It seems as though this could shake out either way.

A very interesting new distributed
filesystem has hit the scene,
created by Sage Weil as part of his PhD studies. It's been under
development for a while now, but Sage has just made his first
official announcement. As a result, the filesystem is likely to be
more stable than other filesystems at the time of their initial
announcement; however, because of the lack of testing, users probably should
not trust Ceph with their data until it
has had a bit more time
under the spotlight.

Ceph supports the familiar POSIX filesystem semantics and distributes
its data across an arbitrary number of nodes on a network. Data is
replicated and rebalanced behind the scenes, so the loss of only a
small number of nodes would be unlikely to cause any data loss.

Originally, the filesystem client itself had been done in FUSE, which
made for rapid development at the cost of some speed and correctness.
One of the reasons Sage chose to make his announcement now is that he
has begun work on an in-kernel client, which addresses all the
correctness and efficiency issues.

Adrian Bunk wants to take away the
Experimental configuration
dependency. The idea behind Experimental was that
users could
choose not to see a large swath of unstable configuration options and, thus, focus only on the options that seemed the most thoroughly tested
and reliable. If, during kernel configuration, users clicked on the
“Enable experimental features” option, they suddenly would see all the
weird stuff that hadn't yet stabilized. The great value of the
Experimental option was that it allowed newer code to have the
widest possible distribution among users, without putting users in a
position to harm themselves by inadvertently enabling a feature that
would somehow or other trash their systems.

Unfortunately, according to Adrian, so many necessary drivers still are
listed as experimental, that distributions have been enabling
experimental features by default in their production kernels. In many
cases, these drivers have not really been experimental for a long time,
but their developers just never bothered to remove the dependency. So
now, users have none of the benefit of being able to turn off
experimental features. If they want to use their system at all, in
many cases, they are obliged to enable experimental features and hope
they don't inadvertently enable something else that is less stable.

It's unclear what ultimately will become of the feature. Clearly,
many experimental features in the kernel would have to be
removed entirely, if there were no way to hide them from users who
wanted only the most solid features. If Adrian does remove the
Experimental option and nothing replaces it, all those features may
lose out on their current high level of availability to new users.
Meanwhile, the drivers that had caused the whole problem by failing to
remove their dependency on the Experimental option would get to stay
in the kernel, because they are not really experimental.

They Said It

Data likes to meet, have sex and make babies, just make sure it happens in
your hotel room.

—Martin Geddes, psd on Twitter, December 6, 2007

Put it all together, and here's what I see happening. In the next few
quarters, low-end Linux-based PCs are going to quickly take over the bottom
rung of computing. Then, as businesses continue to get comfortable with
SaaS (software as a service) and open-source software, the price benefits
will start leading them toward switching to the new Linux/SaaS office
model.

You'll see this really kick into gear once Vista Service Pack 1 appears and
business customers start seriously looking at what it will cost to migrate
to Vista. That Tiffany-level price tag will make all but the most
Microsoft-centric businesses start considering the Linux/SAAS alternative.

Sun will be announcing a multi-year award program in support of fostering
innovation and advancing open source within our Open Source communities.
We'll be providing a substantial prize purse and working with the
communities involved to develop the approach that works best.

The Linux Muse

Convergent Living keeps expanding its portfolio of Companion-branded home
electronics controllers, all of which involve “server-less smart appliances
running rock-solid Linux”. All are intended to work with the company's own
components or with those of many other manufacturers. At the time of this
writing,
Convergent Living's Integrated Mode Subsystem Drivers supported the
following:

21 scene lighting systems.

Ten distributed audio/video multiroom preamps (with two
“coming”).

Five media audio streamers.

14 digital media servers.

Three I/serial-based components.

Four security panels.

Seven automation panels.

Five I cameras, plus “almost any streaming MPEG-3 camera”.

It also supported a pile of Ethernet converters; VGA/USB extenders via
CAT5; a serial
router and communications to thermostats, humidifiers, shade controls,
weather stations; and other “environmental” electronics by
several
manufacturers, over an array of data link types.

Its latest controller is the Companion Muse, which communicates to both the
Net and local home electronics over Wi-Fi. It has a built-in Web browser,
plus the ability to control home systems either through IP (Internet
Protocol) connections or through “translators” that speak through serial,
IR and other interfaces.

The Muse weighs just less than two pounds and runs on an 800MHz LX-800 Geode
processor. It has an 8.4" TFT Active Matrix 800x600 SVGA LCD
touchscreen, talks 802.11b Wi-Fi and plays 16-bit audio through either a
built-in speaker or a headphone jack. It's recharged through a desk cradle
or USB passthrough.

Configuring and integrating widely disparate home electronics tend to be
complex professional work, so Convergent Living sells its components
through professional integrators. Meanwhile, as the line continues to
expand, it demonstrates the handiness of Linux as a solid platform for
integrating just about anything.

New Features at LinuxJournal.com

If you haven't visited us recently, you may have missed Linux
Journal's
Gadget Guy, Shawn Powers, and his video product reviews. Each week, Shawn
has entertained and informed while giving viewers a peek at some
interesting Linux-powered gadgets, such as the popular ASUS Eee PC, the Z2
Zipit Wireless Messenger and the Neuros MPEG-4 recorder. Be sure to come
back to see what other cool toys he will get his hands on.

Also, take a look at the section aptly named “Live from the
Field” to get some interesting perspectives and perhaps even a
behind-the-scenes look at Linux Journal from our very own staff and
advisory board. These folks tend to have some useful information to
share, and you might even get a look at some of their geek gear. After the
holidays, many of us posted photos and videos of our geekiest gifts for all
to see. If you haven't seen these, they are worth checking out and can be found
at www.linuxjournal.com/microblog.

Drop by and write your thoughts in the comments sections or in the
forums. We'd love to hear from you.

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